This invention relates to a variable speed transmission of the friction-drive type, comprising a driving shaft; at least two ball-driving elements; the driving shaft having drive means associated therewith for rotation of the ball-driving elements; first torque-transmitting means connected with the driving shaft and associated with the ball-driving elements for rotating the latter in unison with the drive shaft; first ball means comprising first cage means and at least two balls each of which balls is in rolling contact with the ball-driving elements; driven-shaft means; second ball means comprising second cage means; second torque-transmitting means for transmitting torque from the first ball means to the second ball means; and shifting lever means adapted for shifting the second torque-transmitting means, the first cage and the second cage.
Such variable speed transmissions are well-known, for instance from French Pat. No. 430,318, from British Pat. No. 165,865, from U.S. Pat. Nos. 1,448,490 and 2,444,470 and from Swiss Pat. No. 482,132. These transmissions permit shifting a ball or the like means on the flat surface of a disk or similar rotating mechanical element and transmission of the rolling movement of the ball to a driven shaft and comprise means for shifting the ball from a dead-center position on the disk surface (in which case the driven shaft would stand still and the driving shaft would idle) toward one side of the periphery of the disk which would cause infinitely variable increase in speed, but also a weakening of the transmitted forces. The same occurs when the ball is shifted to the opposite side, toward the periphery of the disk; however, in this case, the sense of rotation of the driven shaft is reversed.
These known transmissions suffer largely from wear, primarily on the disk surface and/or on the ball surface, whereby irregularities therof make it difficult to achieve a dead-center position of the ball on the disk and, consequently, complete standstill of the driven shaft. Also, the force needed for maintaining or for shifting speed increases in proportion to the load and adds to wear of all parts.
Moreover, in order to obtain satisfactory operation, parts such as in particular the disk and ball must be manufactured and assembled with high precision. A minute deviation of the ball-contacting surface of the disk from the vertical position of the shaft bearing the disk in the supporting means needed will lead to serious irregularities contributing to rapid wear.